By LAURAN NEERGAARD and MATTHEW PERRONE
U.S. health advisers are debating if millions of Americans who received Moderna vaccinations should get a booster shot — this time, using half the original dose. Already certain high-risk groups who got their initial Pfizer vaccinations at least six months ago are rolling up their sleeves. Thursday and Friday, advisers to the Food and Drug Administration will recommend if and when to offer boosters to both Moderna and Johnson & Johnson vaccine recipients. Final decisions are expected next week. U.S. officials stress that the priority is to get shots to the 66 million unvaccinated Americans who are eligible.